COMMENTARY – Academics have filled volumes on the differences between what they call public and private goods. Too often the distinction seems to come down to ownership: If something is owned by society as a whole, it is a common good. If owned by one or more individuals, it is a private good. Common goods are things like public schools, parks or roads that are owned by all of society. The responsibility for operating and maintaining them is (usually) assigned to government and supported by tax revenues.

This is the standard pattern for metropolitan roadway systems in the United States. They are built and maintained by a mixture of municipal, county and state governments that fund most of the cost from general tax revenues. They are often supplemented by “user taxes” levied on the purchase of motor-vehicle fuel, which implies that motorists pay based on how much they use the roadways.

But even when a roadway network is supported by fuel taxes, there remains a disconnect in the minds of motorists between the act of driving on roadways and paying for them. This is quite different from commodities distributed through the marketplace, where a consumer must buy and pay for some quantity of a commodity before being able to consume it.

The result is an instinctive sense among motorists that roadways are free.

A useful metaphor popularized by biologist Garret Hardin in 1968 illustrates the basic problem. Imagine a community that has a publicly owned pasture where local farmers can graze their dairy cows without having to pay any user charges. Under these circumstances, each farmer seeks to graze as many cows as possible in the pasture because each additional cow will increase milk production but not feeding cost.

This only works so long as the number of grazing cows remains within the pasture’s feeding capacity. Once the farmers exceed this limit, the pasture’s viability begins to break down. The cows consume its grass faster than it can replenish itself with fresh growth, resulting in less nourishment for each cow.

When farmers are faced with cows that are producing less milk to sell, their logical response is to add still more cows to the overused pasture. When all the farmers do this, the result can only be an increasingly dysfunctional pasture and declining milk production for everyone.

In Hardin’s words: “Therein is the tragedy. Each man is locked into a system that compels him to increase his herd without limit – in a world that is limited. Ruin is the destination towards which all men rush, each pursuing his own best interest in a society that believes in the freedom of the commons.”

Severe traffic congestion is a modern example of the tragedy of the commons. Hardin’s metaphor illuminates a broad range of socioeconomic questions about why congestion afflicts so many metropolitan areas.

Page 2 of 2 - It illustrates the inevitable tendency to overuse common goods that are perceived to be free. It explains why this tendency leads to a condition in which supply never catches up with the demand. It describes how the widespread availability of free public goods can significantly influence the underlying economics of many private activities that come to depend on them. And it demonstrates the relative ease with which an entire society can be locked into counterproductive behaviors.

The most sensible solution to the tragedy of the commons may be to charge farmers grazing fees. This immediately confronts them with a series of critical business judgments about how to maximize their milk revenues, such as how much to spend feeding pasture grass to their cows or whether to feed them corn or other grains instead.

When all forms of cattle feed are distributed at prices that reflect supply and demand, the business of milk production becomes more rational. Perhaps the same is true for metropolitan roadway systems: directly charge motorists for roadway use and the economics of building, operating and maintaining roadways change rapidly – and for the better.

Joseph M. Giglio is a professor of strategic management at Northeastern University’s D’Amore-McKim School of Business.